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SubjectRe: [RFC PATCH v3] perf/x86: make perf callchain work without CONFIG_FRAME_POINTER
On Fri, Apr 19, 2019 at 8:58 AM Josh Poimboeuf <jpoimboe@redhat.com> wrote:
>
> I still don't like using regs->bp because it results in different code
> paths for FP and ORC. In the FP case, the regs are treated like real
> regs even though they're fake.
>
> Something like the below would be much simpler. Would this work? I don't
> know if any other code relies on the fake regs->bp or regs->sp.

Works perfectly. My only concern is that FP path used to work very
well, not sure it's a good idea to change it, and this may bring some
extra overhead for FP path.

>
> (BTW, tomorrow is a US holiday so I may not be very responsive until
> Monday.)
>
> diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c
> index de1a924a4914..f315425d8468 100644
> --- a/arch/x86/events/core.c
> +++ b/arch/x86/events/core.c
> @@ -2382,6 +2382,15 @@ void arch_perf_update_userpage(struct perf_event *event,
> cyc2ns_read_end();
> }
>
> +/*
> + * Determine whether the regs were taken from an irq/exception handler rather
> + * than from perf_arch_fetch_caller_regs().
> + */
> +static bool perf_hw_regs(struct pt_regs *regs)
> +{
> + return regs->flags & X86_EFLAGS_FIXED;
> +}
> +
> void
> perf_callchain_kernel(struct perf_callchain_entry_ctx *entry, struct pt_regs *regs)
> {
> @@ -2393,11 +2402,15 @@ perf_callchain_kernel(struct perf_callchain_entry_ctx *entry, struct pt_regs *re
> return;
> }
>
> - if (perf_callchain_store(entry, regs->ip))
> - return;
> + if (perf_hw_regs(regs)) {
> + if (perf_callchain_store(entry, regs->ip))
> + return;
> + unwind_start(&state, current, regs, NULL);
> + } else {
> + unwind_start(&state, current, NULL, (void *)regs->sp);
> + }
>
> - for (unwind_start(&state, current, regs, NULL); !unwind_done(&state);
> - unwind_next_frame(&state)) {
> + for (; !unwind_done(&state); unwind_next_frame(&state)) {
> addr = unwind_get_return_address(&state);
> if (!addr || perf_callchain_store(entry, addr))
> return;
> diff --git a/arch/x86/include/asm/perf_event.h b/arch/x86/include/asm/perf_event.h
> index 04768a3a5454..1392d5e6e8d6 100644
> --- a/arch/x86/include/asm/perf_event.h
> +++ b/arch/x86/include/asm/perf_event.h
> @@ -308,14 +308,9 @@ extern unsigned long perf_misc_flags(struct pt_regs *regs);
> */
> #define perf_arch_fetch_caller_regs(regs, __ip) { \
> (regs)->ip = (__ip); \
> - (regs)->bp = caller_frame_pointer(); \
> + (regs)->sp = (unsigned long)__builtin_frame_address(0); \
> (regs)->cs = __KERNEL_CS; \
> regs->flags = 0; \
> - asm volatile( \
> - _ASM_MOV "%%"_ASM_SP ", %0\n" \
> - : "=m" ((regs)->sp) \
> - :: "memory" \
> - ); \
> }
>
> struct perf_guest_switch_msr {
> diff --git a/arch/x86/include/asm/stacktrace.h b/arch/x86/include/asm/stacktrace.h
> index d6d758a187b6..a8d0cdf48616 100644
> --- a/arch/x86/include/asm/stacktrace.h
> +++ b/arch/x86/include/asm/stacktrace.h
> @@ -100,19 +100,6 @@ struct stack_frame_ia32 {
> u32 return_address;
> };
>
> -static inline unsigned long caller_frame_pointer(void)
> -{
> - struct stack_frame *frame;
> -
> - frame = __builtin_frame_address(0);
> -
> -#ifdef CONFIG_FRAME_POINTER
> - frame = frame->next_frame;
> -#endif
> -
> - return (unsigned long)frame;
> -}
> -
> void show_opcodes(struct pt_regs *regs, const char *loglvl);
> void show_ip(struct pt_regs *regs, const char *loglvl);
> #endif /* _ASM_X86_STACKTRACE_H */
> diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
> index f3864e1c5569..0f560069aeec 100644
> --- a/include/linux/perf_event.h
> +++ b/include/linux/perf_event.h
> @@ -1062,7 +1062,7 @@ static inline void perf_arch_fetch_caller_regs(struct pt_regs *regs, unsigned lo
> * the nth caller. We only need a few of the regs:
> * - ip for PERF_SAMPLE_IP
> * - cs for user_mode() tests
> - * - bp for callchains
> + * - sp for callchains
> * - eflags, for future purposes, just in case
> */
> static inline void perf_fetch_caller_regs(struct pt_regs *regs)

--
Best Regards,
Kairui Song

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